The present invention relates to printing plates and more particularly to a method of manufacturing a seamless cylindrical printing plate (hereinafter referred to as "a seamless printing roll" when applicable) and an apparatus for practicing the method.
In the case where continuous patterns are printed on wall paper, packing paper or the like, the pictures or patterns of a printing plate on a plate cylinder must be made continuous so that the pictures or patterns appear natural and uninterrupted. In order to accomplish the necessary fine printing operation, heretofore a layer of rubber or polyvinyl chloride was wound around the cylinder and was engraved manually or a rubber printing plate produced by casting was bonded in the form of waves to the cylinder with care that the picture or pattern was not cut but was continuous. However, these conventional methods are disadvantageous in that such methods require much skill in implementation, the patterns are limited, and it takes a long time to produce such a printing roll.
In order to overcome such difficulties, a variety of seamless printing roll manufacturing methods and apparatuses utilizing photosensitive resin printing plates have been proposed in the art. For instance, in a conventional elementary method, a flat printing plate is formed, the flat printing plate is wound around a plate cylinder, and both ends of the printing plate thus wound are joined together by using, for instance, an adhesive agent. (See, for example, Japanese Laid Open patent application Nos. 143404/1978 and 29804/1978). However, this method is disadvantageous in that if the joining portions of the printing plate are intricate, the joining operation can be considerably troublesome and, if the two ends of the printing plate are unsatisfactorily joined together, the printing plate may become detached from the plate cylinder during the printing operation at the joined portion. It should be noted that in this method the resin printing plate merely takes the place of a conventional cast rubber printing plate and that therefore the technique for manufacturing the seamless printing roll is fundamentally the same as the conventional one.
In addition, a method is known with which photosensitive resin is applied directly to a cylinder used as a plate cylinder and the layer of photosensitive resin on the cylinder forms a seamless printing roll. (See, for example, Japanese Patent Publication No. 28042/1977, and Japanese Laid Open Application Nos. 60301/1975, 90404/1975, 62503/1977 and 145703/1978 which relates mainly to coating techniques; and Japanese Patent Application Publication No. 42451/1971 and Japanese Laid Open Patent Application Nos. 504/1977 and 77406/1976 which relates mainly to exposure techniques).
In any of these methods, a photosensitive layer is formed on a cylinder by applying thereto a photosensitive material which is produced by heating solid-state photo-sensitive thermoplastic resin or dissolving the material in a solvent, or by applying a photosensitive resin solution thereto. The photosensitive layer is then placed in semi-hardened state by subjecting it to exposure. In other words, in such methods, a photosensitive layer is formed on a cylinder and then the photosensitive layer thus formed is exposed through a negative or positive film. In order to manufacture a seamless printing roll according to these methods, two manufacturing steps, a step of forming the photosensitive layer and a step of exposing the photosensitive layer to light, are required. Thus, in view of both total effort required and economy, these methods are low in efficiency.
In addition, as a result of the development of laser beams, a method of manufacturing a seamless printing roll utilizing laser beams has been proposed. However, in order to practice this technique, it is necessary to use an extremely expensive apparatus and accordingly a seamless printing roll manufactured by the apparatus is necessarily high in cost. With respect to the image reproducibility on such a printing roll, it is rather difficult to provide the reproducibility equivalent to that of the conventional cast printing plate. Thus, the method has not been completely accepted as yet.
In addition, printing of a continuous pattern is carried out by employing a photogravure roll. However, with the advent of light sensitive resin plate, gravure printing is gradually being abandoned in favor of relief printing because the production of a gravure roll is costly and may cause a heavy metal effluent.
Accordingly, an object of this invention is to eliminate the above-described difficulties accompanying conventional methods. More specifically, an object of the invention is to provide a seamless printing roll manufacturing method and apparatus in which a photosensitive layer is formed and exposed to light simultaneously in a single process thereby to readily and quickly to form a seamless printing roll which is accordingly low in cost.